The invention relates generally to digital image capture systems, and more particularly to the packaging of image sensors in conjunction with imaging optics.
Digital image capture systems utilize image sensors to capture digital image information. As with conventional film based image capture systems, digital image capture systems utilize imaging optics and an aperture to direct light onto the image capture medium. Many new high volume applications of digital image capture systems require image sensors and imaging optics that are small and easy to assemble.
In order to ensure the quality of images generated from a digital image capture system, it is important that only a controlled amount of light is able to contact the image sensor. In order to control the amount of light that contacts the image sensor, the image sensor is sealed in a light-tight environment with image bearing light passing through a lens aperture. Light contacting the image sensor from any other location will degrade the quality of the captured images.
In order to make digital image capture systems that are easy to assemble, it is important that the image sensor chips can be packaged with standard packaging techniques, such as wire bonding, and that the image sensor packages can be attached to circuit boards utilizing standard automated mounting techniques, such as widely utilized surface mounting techniques.
It is also important in digital image capture systems that the imaging optics be accurately aligned with the image sensor so that the image bearing light is focused onto the image sensor. One technique for accurately aligning the imaging optics with the image sensor involves powering up the image sensor and adjusting the location of the imaging optics in response to a detected image. Powering up the image sensor to align the imaging optics is time consuming and requires specialized alignment equipment.
Various techniques are known for integrating imaging optics with an image sensor. One prior art digital image capture system involves a lens system that is attached directly to the surface of an image sensor. FIG. 1 is an example depiction of a digital image capture system in which a lens system is attached directly to the surface of an image sensor. The digital image capture system includes a printed circuit board 104, an image sensor package 102, an image sensor chip 110, wire bonds 106, package leads 112, a lens system 120 and 124, a lens aperture 122, and an opaque encapsulant 126. As shown in FIG. 1, the lens system is attached directly to the surface of the image sensor and the opaque encapsulant is utilized to fill in the space between the lens system and the image sensor package. Alternatively, the lens system may be aligned by contact with the image sensor but not attached directly to the image sensor. The arrangement of image capture elements works well to prevent unwanted light from contacting the image sensor and can provide accurate alignment between the image sensor and the lens system. Although the image capture system can prevent unwanted light from contacting the image sensor and provide accurate alignment between the image sensor and the lens system, the arrangement of image capture elements is not well suited to high-volume assembly processes, such as wire boding, because the lens system hinders the wire bonding process or may damage existing wire bonds during placement of the lens system.
Another prior art digital image capture system involves attaching an image sensor package to a circuit board and then attaching an imaging optics system directly to the same circuit board around the outer edges of the image sensor package. FIG. 2 is an example depiction of a digital image capture system in which imaging optics and an image sensor package are attached to the same circuit board. The digital image capture system includes a circuit board 204, an image sensor package 202, an image sensor chip 210, wire bonds 206, connection leads 212, an image sensor cover glass 214, a light shield 226, an infra-red filter 224, a filter retaining ring 228, a lens attachment structure 230, lens attachment screws 232, a lens holder 218, lens elements 220, and a lens aperture 222. Although the arrangement of image capture elements works well, the technique requires many additional parts which add cost to the overall image capture system. In addition, the circuit board must be designed and built with precisely aligned attachment holes for attaching the imaging optics. Even with precisely aligned holes for attaching the imaging optics, the image sensor package must be mounted on the circuit board with precise accuracy in order to ensure alignment between the imaging optics and the image sensor. Further, the attachment structure of the imaging optics extends beyond the outer edges of the image sensor package, thereby taking up valuable circuit board real estate. Another disadvantage of the image capture structure is that it is difficult to get the rear lens element close to the image sensor because the image sensor cover glass is in the way.
The description of prior art image capture systems is not meant to be exhaustive although it does highlight some of the problems involved with assembling image capture systems, such as high volume digital cameras, that utilize image sensor chips and imaging optics. In view of the problems involved with assembling image capture systems, what is needed is an economic and reliable technique for assembling a digital image capture system.
A digital image capture system includes an image sensor package and a powered lens element that is attached to the image sensor package. The image sensor package includes an image sensor, a package structure for holding the image sensor, and electrical connectors for creating electrical connection between the image sensor and a circuit board. The package structure and the powered lens element include complementary surfaces that enable the powered lens element to be attached to the image sensor package.
Preferably, the powered lens element is glued to the package structure to create a sealed environment for the image sensor. In an embodiment, a temporary protective cover is attached to the powered lens element to protect the powered lens element during attachment of the image sensor package to the circuit board.
In an embodiment of the digital image capture system, an additional powered lens element is attached to the first powered lens element to create a composite lens element.
In an embodiment of the digital image capture system, the powered lens element includes an opaque surface that prevents unwanted light from contacting the image sensor. The powered lens element also includes a light input and a light output that enable light traveling in desired paths to pass through the powered lens element and contact the image sensor.
In an embodiment of the digital image capture system, an optically powered portion of the powered lens element is located on the rear surface of the powered lens element near the image sensor.
In an embodiment of the digital image capture system, the package structure includes alignment features for aligning the powered lens element with the package structure.
An advantage of the digital image capture system is that no additional lens mounting structures are required to attach a powered lens element to the image sensor package. Another advantage is that the lens element can be located close to the image sensor because the lens element takes the place of the rear cover glass. In addition, the digital image capture system is compatible with known chip packaging and surface mounting techniques that are utilized for high-volume electronic devices.
Another digital image capture system includes an image sensor package, an unpowered transparent cover element attached to the image sensor package, and a powered lens element attached to the unpowered transparent cover element. The image sensor package includes an image sensor, a package structure for holding the image sensor, and electrical connectors for creating electrical connection between the image sensor and a circuit board. The package structure and the unpowered transparent cover element include complementary surfaces that enable the unpowered transparent cover element to be attached to the image sensor package.
Preferably, the unpowered transparent cover element is glued to the package structure to create a sealed environment for the image sensor and the powered lens element is glued to the unpowered transparent cover element. The powered lens element can be glued to the unpowered transparent cover element after the image sensor package is soldered to the circuit board. In an embodiment, a temporary protective cover is attached to the unpowered transparent cover element or the powered lens element to protect the unpowered transparent cover element or the powered lens element during attachment of the image sensor package to the circuit board.
An advantage of the digital image capture system is that the image sensor package can be mounted to the circuit board before the powered lens element is attached to the unpowered transparent cover element, thereby preventing the powered lens element from being exposed to the high temperatures of circuit board assembly.
Another digital image capture system includes an image sensor, a package structure for holding the image sensor, and electrical connectors for creating electrical connections between the image sensor and a circuit board. The package structure includes a surface that is complementary to a surface of a temporary protective cover and a surface of a powered lens element. The surface of the package structure allows a temporary protective cover and then a powered lens element to be attached to the package structure. In an embodiment, the temporary protective cover is attached to the package structure while the electrical connectors are attached to the circuit board. The temporary protective cover is then replaced by the powered lens element after the electrical connectors are attached to the circuit board. An advantage of the digital image capture system is that the image sensor package can be mounted to the circuit board while the image sensor is protected by the temporary protective cover instead of the powered lens element, thereby preventing the powered lens element from being exposed to the high temperatures of circuit board assembly.